curry recipe question--urad dal

In a message dated 97-05-30 09:10:42 EDT, you write:
<< The following is a way of making curries which is quick, simple, adapts to
various vegetables, and is delicious. This is a south Indian style and for
those of you who have had only brownish, oily glop at Indian restaurants,
this recipe should be a real treat!
1 tsp cumin seeds
1 tsp black mustard seeds
1 tsp whole fenugreek
2 tsp urad dal (avail. in Indian groceries--it's white in its split form,
which is what you want)
1 onion, chopped >>
that sounds like a great recipe-- i love using whole spices. where does the
urad dal fit in? do you add it with the onions??? is it to serve as a
thickener?
there's a wonderful Indian grocery in Arlington called "Indian Spices and
Appliances" (love the name!) on Wilson Blvd between Ballston and Clarendon.
they have all these spices and more. joanna in dc
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